The present invention generally relates to technologies for displaying images by irradiating a light flux from a light source onto a display device such as a transmissive or reflective type liquid panel or a panel with very small mirrors, and particularly to a front-type or rear-type projection display apparatus or television apparatus for reproducing color images by modulating the amounts of color light in a color sequential manner.
There is a known projection-type display apparatus in which images can be displayed in such a manner that the amounts of the light fluxes emitted from the light source side and transmitted through or reflected from a transmissive or reflective liquid crystal panel can be controlled in accordance with the gradation levels of the inputted image data. There is also another known projection type display apparatus that has a reflective panel formed of a number of very small mirrors of which the number corresponds to that of all the pixels for the display so that the contrast and the utilization ratio of light can be improved. For example, documents of, for example, JP-A-10-78550 and JP-A-2000-259127 describe a projection type display apparatus having a reflective display device formed of very small mirrors.
In this display apparatus, the gradients of the very small mirrors arranged in a two-dimensional manner to oppose the respective pixels are controlled (to be on or off) so that light can be reflected (on) or not (off) from the mirrors into the projection lens to reproduce an image. The rate of the on/off time of the very small mirrors and the integral effect of visual sense within the frame period (for example, about 16.7 m sec when 60 Hz is used) as an image unit to be displayed are utilized to achieve the gradation expression.
In this case, the reproducible gradation number depends on the speed of controlling the very small mirrors. In addition, each of the very small mirrors is switched to one of the red (R), green (G) and blue (B) in a time-division manner to reproduce a color image. The construction of the apparatus is thus determined according to the use. Moreover, the reproducible gradation number is increased by employing the area gradation using the error diffusing method/dither method approach. Also, a technique is proposed for amplifying white brightness by making effective use of the very small mirrors in time axis.
Another display apparatus is proposed as described in JP-A-8-101387, in which the contrast is adjusted to improve the image reproducibility by switching a plurality of light sources including a lamp light source and LEDs and by appropriately changing the transmission factor of the display device.
In the case of those projection type display apparatus using such display devices, the light source is actually a Xenon lamp or metal halide lamp because it is desired to be a point light source from the light concentration point of view and excellent in spectrum, to have a high emission efficiency and a long life, and to provide uniform light intensity with less irregular emission.
Recently, the performance of LED has been improved in color emission, brightness and life span, and thus the use of LED has been expanded to the backlight of different display apparatus, and traffic lights.